A conventional, automatically operable sprinkler comprises a supporting frame having a body formed of relatively non-corrosive metal that is adapted to be coupled to a water or other fire extinguishing fluid pipe in such position as to enable the sprinkler, when actuated, to discharge pressurized fluid in a pattern which, in conjunction with other sprinklers, enables the fluid to saturate a selected area. A conventional sprinkler includes a closure for the fluid passage which normally seals the passage and prevents the flow of fluid therethrough. The closure is maintained in its passage-sealing position by means of a collapsible strut which bears against the closure and a part of the sprinkler frame spaced from the closure. Such a sprinkler frame includes a pair of spaced apart legs joined at corresponding ends to the body and at their opposite ends by a cross bar provided with an adjusting screw that is movable toward and away from the closure and which bears against the opposite end of the strut.
The strut typically is one which includes a eutectic substance that reacts in response to a rise in its temperature to a predetermined level to cause the strut to collapse, thereby removing the restraining force on the closure, whereupon the pressure of fluid in the sprinkler system is able to unseat the closure and permit fluid to flow through the passage for discharge in the selected pattern. In most instances the fluid issuing from the passage impinges upon a deflector which causes the fluid to be discharged in the desired pattern.
A sprinkler of the kind referred to has the disadvantage that the legs of the supporting frame lie in the path of fluid discharged from the passage. Consequently, some of the fluid discharged from the frame passage impinges upon the arms and causes gaps in the coverage pattern.
In many instances the collapsible strut that is used to maintain the closure in its passage-sealing position comprises a glass tube within which is sealed a liquid which expands in response to its reaching a predetermined increased temperature level so as to rupture the glass tube, thereby enabling the closure to move off its passage-sealing seat. Although the glass forming the bulb is quite strong, the necessity of having to apply a direct force on the bulb to enable it to maintain the closure in its passage-sealing position makes possible the application of either too much or too little force on the bulb. If too much force is applied, the bulb may break prematurely. If too little force is applied, changes in temperature of the associated parts and differences in coefficients of thermal expansion of the several parts of the sprinklers can cause a passage-sealing closure to leak.
Some of the conventional sprinklers utilizing collapsible or frangible glass bulb struts have one end thereof seated directly on the passage-sealing closure. In many instances such a closure is in direct contact with the fire extinguisher fluid contained in the fluid system. In those instances in which the closure is of good thermal conductivity, heat from the strut is transmitted through the closure to the extinguishing fluid. Since the temperature of the extinguishing fluid usually is lower than that at which the strut collapses, the strut is cooled because of its contact with the closure. Consequently, the strut does not always collapse at the predetermined temperature, but must be heated to an even higher temperature in order to function properly.